High refractive index pressure-sensitive adhesives

ABSTRACT

The present invention provides pressure-sensitive adhesives having a refractive index of at least 1.48. The pressure-sensitive adhesives comprise at least one monomer containing a substituted or an unsubstituted aromatic moiety.

RELATED APPLICATION DATA

This application is a continuation of application Ser. No. 10/701,218,filed Nov. 4, 2003, now allowed, which is a divisional of applicationSer. No. 09/605,500 filed Jun. 28, 2000, and issued as U.S. Pat. No.6,663,978.

FIELD OF INVENTION

This invention relates to pressure-sensitive adhesives. Moreparticularly, this invention relates to pressure-sensitive adhesiveshaving a high refractive index.

BACKGROUND OF THE INVENTION

Pressure-sensitive adhesives (“PSAs”) are defined herein as adhesiveswhich exhibit permanent tack at room temperature. This property allowspressure-sensitive adhesives to adhere tenaciously upon application withonly light finger pressure. PSAs have a balance of properties: adhesion,cohesion, stretchiness, and elasticity. Adhesion refers both toimmediate adhesion to a surface and to the bond strength which developsupon application of pressure (often measured as “peel strength”).Cohesion refers to the “shear strength” or resistance of the applied PSAto failure when subjected to shearing forces. Stretchiness refers to theability to elongate under low stresses. Elasticity refers to a propertywherein the material exhibits a retractive force when stretched andretracts when the force is released.

Pressure-sensitive adhesives have many diverse applications includingapplications in optical products. For certain optical applications, itis useful to match the refractive index (RI) of the adhesive to that ofthe substrate to which it is applied. This matching of refractive indexenhances the optical properties of the construction by reducing glareand reflectance. Glare is defined herein as the average reflectance overa range of 450-650 nanometers and reflectance is defined herein as theprocess where a fraction of the radiant flux incident on a surface isreturned into the same hemisphere whose base is the surface and whichcontains the incident radiation (see Handbook of Optics, 2^(nd) ed.,McGraw-Hill, Inc., 1995). Often, the substrate is a polymeric materialhaving refractive indexes in the range of 1.48 to 1.65, for example,polymethyl(meth)acrylate (PMMA) has a RI of 1.489; polycarbonate has aRI of 1.585; and polyethylene terephthalate (PET) has a RI of 1.64.

Known PSAs have RIs of about 1.47 or less. If these PSAs are used inoptical applications, glare and reflectance may occur.

Therefore, the need exists for pressure-sensitive adhesives which havehigh refractive indexes.

SUMMARY OF THE INVENTION

The present invention provides pressure-sensitive adhesives which have arefractive index of at least 1.48. These pressure-sensitive adhesivesare particularly suitable for optical applications where the substratesimilarly has a high refractive index. The pressure-sensitive adhesivesof the present invention advantageously allow for the matching ofrefractive index which reduces glare and reflectance.

The pressure-sensitive adhesives of the present invention comprise atleast one monomer containing a substituted or an unsubstituted aromaticmoiety.

One aspect of the present invention is a pressure-sensitive adhesivecomprising the reaction product of: (a) at least one monomer selectedfrom the group consisting of a monomeric acrylic or methacrylic acidester of a non-tertiary alcohol, the alkyl group of which comprises fromabout 1 to about 12 carbon atoms, preferably from about 4 to about 8carbons; and (b) at least one monomer containing a substituted or anunsubstituted aromatic moiety.

Another aspect of the present invention is a pressure-sensitive adhesivecomprising the reaction product of: (b) at least one monomer containinga substituted or an unsubstituted aromatic moiety; and (c) at least onepolar monomer copolymerizable with component (b).

Yet, another aspect of the present invention is a pressure-sensitiveadhesive comprising the reaction product of: (a) at least one monomerselected from the group consisting of a monomeric acrylic or methacrylicacid ester of a non-tertiary alcohol, the alkyl group of which comprisesfrom about 1 to about 12 carbon atoms, preferably from about 4 to about8 carbons; (b) at least one monomer containing a substituted orunsubstituted aromatic moiety; and (c) at least one polar monomercopolymerizable with the monomer(s) of components (a) and (b).

The pressure-sensitive adhesives of the present invention may optionallycomprise other monomers, crosslinkers, and additives.

Another embodiment of the present invention is a substrate coated withthe pressure-sensitive adhesives of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention relates to pressure-sensitive adhesives having arefractive index of at least 1.48. Preferably, the pressure-sensitiveadhesives have a refractive index of at least 1.50.

The pressure-sensitive adhesives of the present invention have a highrefractive index and yet have a good balance of the four propertiesrelevant for pressure-sensitive adhesives: adhesion, cohesion,stretchiness, and elasticity.

Refractive index is defined herein as the absolute refractive index of amaterial (e.g., a monomer) which is understood to be the ratio of thespeed of electromagnetic radiation in free space to the speed of theradiation in that material, with the radiation being of sodium yellowlight at a wavelength of about 583.9 nanometers (nm). The refractiveindex can be measured using known methods and is generally measuredusing an Abbe Refractometer.

The pressure-sensitive adhesives of the present invention are acrylateadhesives comprising at least one aromatic monomer which is eithersubstituted or unsubstituted. The pressure-sensitive adhesives mayfurther comprise at least one acrylic monomer selected from the groupconsisting of a monomeric acrylic or methacrylic acid ester of anon-tertiary alcohol and/or at least one polar monomer. Thepressure-sensitive adhesives of the present invention optionallycomprise other monomers which may be added to improve the properties ofthe adhesives, such as crosslinkers, and other additives such astackifiers or plasticizers.

Acrylic Monomers

The acrylic monomers useful in the pressure-sensitive adhesive of thepresent invention are typically present at ranges from about 0 to about93 parts by weight. Useful acrylic monomers include at least one monomerselected from the group consisting of a monomeric acrylic or methacrylicacid ester of a non-tertiary alkyl alcohol, the alkyl group of whichcomprises from about 1 to about 12 carbon atoms, preferably from about 4to about 8 carbon atoms, and mixtures thereof.

Suitable acrylic monomers include, but are not limited to, thoseselected from the group consisting of the esters of acrylic acid ormethacrylic acid with non-tertiary alkyl alcohols such as 1-butanol,1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol,1-methyl-1-butanol, 1-methyl-1-pentanol, 2-methyl-1-pentanol,3-methyl-1-pentanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 2-octanol, 1-decanol,1-dodecanol, and the like, and mixtures thereof. Such monomeric acrylicor methacrylic esters are known in the art and are commerciallyavailable.

Aromatic Monomers

The following aromatic monomers are high refractive index acrylicmonomers, preferably all of which have homopolymer glass transitiontemperatures at or below 50° C. These aromatic monomers, whenpolymerized alone or in the presence of other acrylic monomers, resultin PSAs having RIs higher than are otherwise available. By adjusting theratio of monomers, it is possible to make PSAs having RIs of at least1.48.

The aromatic monomers of the present invention are represented by thefollowing general Formula (I):

wherein:

-   -   Ar is an aromatic group which is unsubstituted or substituted        with a substituent selected from the group consisting of Br_(y)        and (R³)_(z)        -   wherein y represents the number of bromine substituents            attached to the aromatic group and is an integer from 0 to            3;        -   R³ is a straight or branched alkyl of 2 to 12 carbons; and        -   z represents the number of R³ substituents attached to the            aromatic ring and is an integer from 0 to 1,            -   provided that both y and z are not zero;        -   X is either oxygen or sulfur;        -   n is 0 to 3, preferably n is 0 or 1;        -   R¹ is an unsubstituted straight or branched alkyl linking            group of 2 to 12 carbons, preferably 2 to 8 carbons; and        -   R² is either H or CH₃.

In one embodiment of aromatic monomers, X is oxygen. Within thisembodiment of aromatic monomers, a group of monomers includes those ofFormula (III) wherein Ar is naphthyl:

and R¹, R², and n are as defined above. The naphthyl group isunsubstituted or substituted as described above. Within the group ofnaphthyl aromatic monomers, another group is that wherein Ar is1-napthyl or 2-napthyl.

Within the embodiment of aromatic monomers where X is oxygen, anothergroup of monomers includes those of Formula (III) wherein Ar is phenyl:

and R¹, R², and n are as defined above. The phenyl group isunsubstituted or substituted as described above. Within the substitutedgroup of phenyl aromatic monomers, preferably the phenyl is dibromosubstituted. Within the bromine substituted group, the phenyl monomersmay also be 2-alkyl substituted or 4-alkyl substituted.

In an additional embodiment of aromatic monomers, X is sulfur. Withinthis embodiment of aromatic monomers, a group of monomers includes thoseof Formula (IV) wherein Ar is naphthyl:

and R¹, R², and n are as defined above. The naphthyl group isunsubstituted or substituted as described above. Within the group ofnaphthyl aromatic monomers, an additional group is that wherein Ar is1-napthyl or 2-napthyl.

Within the embodiment of aromatic monomers where X is sulfur, anothergroup of monomers includes those of Formula (V) wherein Ar is phenyl:

and R¹, R², and n are as defined above. The phenyl group isunsubstituted or substituted as described above. Within this group ofphenyl aromatic monomers, preferably the phenyl is dibromo substituted.In another group, the phenyl monomers may be 2-alkyl substituted or4-alkyl substituted.

Specific examples of aromatic monomers suitable in the present inventioninclude, but are not limited to, 6-(4,6-dibromo-2-isopropylphenoxy)-1-hexyl acrylate, 6-(4,6-dibromo-2-sec-butyl phenoxy)-1-hexylacrylate, 2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecylphenyl acrylate, 2-(1-naphthyloxy)-1-ethyl acrylate,2-(2-naphthyloxy)-1-ethyl acrylate, 6-(1-naphthyloxy)-1-hexyl acrylate,6-(2-naphthyloxy)-1-hexyl acrylate, 8-(1-naphthyloxy)-1-octyl acrylate,8-(2-naphthyloxy)-1-octyl acrylate, 2-phenylthio-1-ethyl acrylate, andphenoxy ethyl acrylate.

Polar Monomers

Polar monomers can be used to increase the cohesive strength of thepressure-sensitive adhesive. Generally, polar monomers are typicallypresent at ranges from about 0 to about 12 parts by weight, preferablyfrom about 2 to about 8 parts by weight. Useful polar monomers include,but are not limited to, those selected from the group consisting ofethylenically unsaturated carboxylic acids, ethylenically unsaturatedsulfonic acids, and ethylenically unsaturated phosphoric acids, andmixtures thereof. Examples of such compounds include, but are notlimited to, those selected from the group consisting of acrylic acid,methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconicacid, maleic acid, B-carboxyethyl acrylate, sulfoethyl methacrylate, andthe like, and mixtures thereof.

Other useful copolymerizable polar monomers include, but are not limitedto, acrylamides, N,N-dialkyl substituted acrylamides, N-vinyl lactams,and N,N-dialkylaminoalkyl acrylates, and mixtures thereof. Illustrativeexamples include, but are not limited to, those selected from the groupconsisting of N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide,N,N-diethyl acrylamide, N,N-diethyl methacrylamide,N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylmethacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropylacrylate, and the like, and mixtures thereof.

Preferred polar monomers include acrylic acid, methacrylic acid,itaconic acid, acrylamide, methacrylamide, acrylonitrile,methacrylonitrile, and mixtures thereof.

Crosslinkers

In order to increase the shear or cohesive strength of the PSAs, acrosslinking additive may be incorporated into the PSA.

Two main types of crosslinking additives are commonly used. The firstcrosslinking additive is a thermal crosslinking additive such as amultifunctional aziridine. One example is 1,1′-(1,3-phenylenedicarbonyl)-bis-(2-methylaziridine) (CAS No. 7652-64-4), referred toherein as “Bisamide”. Such chemical crosslinkers can be added intosolvent-based PSAs after polymerization and activated by heat duringoven drying of the coated adhesive.

In another embodiment, chemical crosslinkers which rely upon freeradicals to carry out the crosslinking reaction may be employed.Reagents such as, for example, peroxides serve as a source of freeradicals. When heated sufficiently, these precursors will generate freeradicals which bring about a crosslinking reaction of the polymer. Acommon free radical generating reagent is benzoyl peroxide. Free radicalgenerators are required only in small quantities, but generally requirehigher temperatures to complete a crosslinking reaction than thoserequired for the bisamide reagent.

The second type of chemical crosslinker is a photosensitive crosslinkerwhich is activated by high intensity ultraviolet (UV) light. Two commonphotosensitive crosslinkers used for hot melt acrylic PSAs arebenzophenone and copolymerizable aromatic ketone monomers as describedin U.S. Pat. No. 4,737,559. Another photocrosslinker, which can bepost-added to the solution polymer and activated by UV light is atriazine, for example,2,4-bis(trichloromethyl)-6-(4-methoxy-pheynl)-s-triazine. Thesecrosslinkers are activated by UV light generated from artificial sourcessuch as medium pressure mercury lamps or a UV blacklight.

Hydrolyzable, free-radically copolymerizable crosslinkers, such asmonoethylenically unsaturated mono-, di-, and trialkoxy silane compoundsincluding, but not limited to, methacryloxypropyltrimethoxysilane(available from Gelest, Inc., Tullytown, Pa.),vinyldimethylethoxysilane, vinylmethyldiethoxysilane,vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriphenoxysilane, andthe like, are also useful crosslinking agents.

Multi-functional acrylates are useful for bulk or emulsionpolymerization. Examples of useful multi-functional acrylatecrosslinking agents include, but are not limited to, diacrylates,triacrylates, and tetraacrylates, such as 1,6-hexanediol diacrylate,poly(ethylene glycol) diacrylates, polybutadiene diacrylate,polyurethane diacrylates, and propoxylated glycerin triacrylate, andmixtures thereof.

Crosslinker is typically present from 0 to about 1 part by weight basedon 100 parts by weight adhesive solids.

Crosslinking may also be achieved using high energy electromagneticradiation such as gamma or e-beam radiation. In this case, nocrosslinker may be required.

Chain Transfer Agent

The present invention may optionally further comprise a chain transferagent. Examples of useful chain transfer agents include, but are notlimited to, those selected from the group consisting of carbontetrabromide, mercaptans, alcohols, and mixtures thereof.

Other Monomers

Other monomers may be added to improve performance, reduce cost, etc. inquantities which do not render the pressure-sensitive adhesivenon-tacky. Examples of such other monomers include vinyl esters, vinylacetate, 2-hydroxyethyl acrylate, styrene, and the like.

Additives

Following copolymerization, other additives may be blended with theresultant acrylate or methacrylate copolymer. For example, compatibletackifiers and/or plasticizers may be added to aid in optimizing theultimate tack and peel properties of the PSA. The use of suchtack-modifiers is common in the art, as is described in the Handbook ofPressure-Sensitive Adhesive Technology, edited by Donatas Satas (1982).Examples of useful tackifiers include, but are not limited to, rosin,rosin derivatives, polyterpene resins, coumarone-indene resins, and thelike. Plasticizers which may be added to the adhesive of the inventionmay be selected from a wide variety of commercially available materials.In each case, the added plasticizer must be compatible with the PSA.Representative plasticizers include polyoxyethylene aryl ether, dialkyladipate, 2-ethylhexyl diphenyl phosphate, t-butylphenyl diphenylphosphate, di(2-ethylhexyl) adipate, toluenesulfonamide, dipropyleneglycol dibenzoate, polyethylene glycol dibenzoate, polyoxypropylene arylether, dibutoxyethoxyethyl formal, and dibutoxyethoxyethyl adipate. Whenused, tackifiers are preferably added in an amount not to exceed about150 parts by weight per 100 parts by weight copolymer, and plasticizermay be added in an amount up to about 50 parts by weight per 100 partsby weight copolymer.

Polymerization Methods

Adhesives useful in this invention can be polymerized by conventionalfree-radical polymerization methods. Suitable methods of polymerizationinclude solution polymerization, suspension polymerization, emulsionpolymerization, and bulk polymerization.

Substrates

The PSAs of the present invention may be coated upon a variety offlexible and inflexible backing materials using conventional coatingtechniques to produce PSA-coated sheet materials. Flexible substratesare defined herein as any material which is conventionally utilized as atape backing or may be of any other flexible material. Examples include,but are not limited to, paper, plastic films such as polypropylene,polyethylene, polyvinyl chloride, polyester (polyethyleneterephthalate), polycarbonate, polymethyl(meth)acrylate (PMMA),cellulose acetate, cellulose triacetate, and ethyl cellulose.Additionally, flexible substrates include, but are not limited to, wovenfabric formed of threads of synthetic or natural materials such ascotton, nylon, rayon, glass, or ceramic material, or they may benonwoven fabric such as air-laid webs or natural or synthetic fibers orblends of these. Examples of inflexible substrates include, but are notlimited to, metal, metallized polymeric film, or ceramic sheet material.The PSA-coated sheet materials may take the form of any articleconventionally known to be utilized with PSA compositions such aslabels, tapes, signs, covers, marking indices, and the like.

Method of Application

The PSAs of the present invention may be coated using a variety ofconventional coating techniques such as roll coating, knife coating, orcurtain coating. The PSAs may also be coated without modification byextrusion, coextrusion, or hot melt techniques by employing suitableconventional coating devices. Primers may be used, but they are notalways necessary. The resultant coatings do not require curing orcrosslinking. However, if enhancement of resistance to solvents, etc.,is desired, crosslinking may be effected by standard methods well-knownin the art, such as radiation curing (electron beam or ultravioletlight) or chemical crosslinking.

EXAMPLES

The present invention will be further described with reference to thefollowing non-limiting examples and test methods. All parts,percentages, and ratios are by weight unless otherwise specified. TABLEOF COMPONENTS Abbreviation Name Available From BA n-butyl acrylate BASFCorporation, Parsippany, NJ AA acrylic acid BASF Corporation,Parsippany, NJ PEA phenoxy ethyl acrylate Sartomer Co., West Chester, PAIOA iso-octyl acrylate CPS Chemical Co., Old Bridge, NJ IRGACURE ™ 6512,2-dimethoxy-1,2- Ceiba-Geigy, Hawthorne, diphenylethan-1-one NY TPO(Lucirin TPO) diphenyl (2,4,6-trimethylbenzoyl) BASF Corporation,phosphine oxide Charlotte, NC EB 9220 hexafunctional aromatic urethaneUCB Chemicals Corp., acrylate Smyrna, GA 2-isopropylphenol and 2-sec-Schenectedy International, butylphenol Schenectedy, NY bromine AldrichChemical ethyl acetate Company Inc, Milwaukee, aqueous sodiumhydrosulfite WI aqueous sodium carbonate sodium iodide 6-chlorohexanolt-butyl methyl ether HCl 6-iodohexanol Toluene Hydroquinone p-toluenesulfonic acid 4-nonylphenol Phenothiazine 1-naphthol ethylene carbonateTriethylamine acryloyl chloride para-toluene sulfonic acid4-methoxyphenol or methyl hydoquinone 2-(phenylthio)ethanol NPALtris(N-nitroso-N-phenylhydroxyl ChemFirst Fine Chemicals, amine)aluminum salt Pascagoula, MS VAZO ™ 672,2′-azobis(2-methylbutanenitrile) E.I. Du Pont De Nemours and Company,Wilmington, DE N,N′-bis-1,2- Xian Modern Chemistrypropyleneisophthalamide Research Institute of China, Xi'an, ChinaRHODOCAL DS-10 ™ Sodium dodecylbenzene sulfonate Rhone-Poulenc NorthAmerican Chem., Cranbury, NJ K₂S₂O₈ J.T. Baker Co., Phillipsburg, NJ

Test Methods

The test methods used to evaluate the PSA coated flexible sheetmaterials of the examples are industry standard tests. The standardtests are described in various publications of the American Society forTesting and Materials (ASTM), Philadelphia, Pa., and the PressureSensitive Tape Council (PSTC).

Shear Strength (ASTM: D3654-78; PSTC-7)

The shear strength is a measure of the cohesiveness or internal strengthof an adhesive. It is based upon the amount of force required to pull anadhesive strip from a standard flat surface in a direction parallel tothe surface to which it has been affixed with a definite pressure. It ismeasured in terms of time (in minutes) required to pull a standard areaof adhesive coated sheet material from a stainless steel test panelunder stress of a constant, standard load.

The tests were conducted on adhesive-coated strips applied to astainless steel panel such that a 12.7 mm by 12.7 mm portion of eachstrip was in firm contact with the panel with one end portion of thetape being free. The panel with coated strip attached was held in a racksuch that the panel forms an angle of 178° with the extended tape freeend which is then tensioned by application of a force of one kilogramapplied as a hanging weight from the free end of the coated strip. The2° less than 180° is used to negate any peel forces, thus insuring thatonly the shear forces are measured, in an attempt to more accuratelydetermine the holding power of the tape being tested. The time elapsedfor each tape example to separate from the test panel is recorded as theshear strength. Unless otherwise noted, all shear failures reportedherein are cohesive failures of the adhesive.

Peel Adhesion (ASTM D3330-78 PSTC-1 (11/75))

Peel adhesion is the force required to remove a coated flexible sheetmaterial from a test panel measured at a specific angle and rate ofremoval. In the examples, this force is expressed in Newtons per 100 mm(N/100 mm) width of coated sheet. The procedure followed is:

1. A 12.7 mm width of the coated sheet is applied to the horizontalsurface of a clean glass test plate with at least 12.7 lineal cm in firmcontact. A 2 kg hard rubber roller is used to apply the strip.

2. The free end of the coated strip is doubled back nearly touchingitself so the angle of removal will be 180°. The free end is attached tothe adhesion tester scale.

3. The glass test plate is clamped in the jaws of a tensile testingmachine which is capable of moving the plate away from the scale at aconstant rate of 2.3 meters per minute.

4. The scale reading in Newtons is recorded as the tape is peeled fromthe glass surface. The data is reported as the average of the range ofnumbers observed during the test.

Measurement of Refractive Index

The refractive index of the pressure-sensitive adhesives and cured filmswere measured using an Abbe Refractometer, Made by Erma Inc., of Tokyo,Japan and distributed by Fisher Scientific.

Monomer Preparation

1. Synthesis of 6-(4,6-dibromo-2-isopropylphenoxy)-1-hexyl acrylate(DBiPPHA)

In a 12 liter round bottom flask equipped with a mechanical stirrer,condenser, nitrogen cap, addition funnel and temperature probe, 1400grams of 2-isopropylphenol was mixed with 4630 grams of deionized water.The mixture was stirred with a mechanical mixer and purged with nitrogenfor about 10 minutes. 3417 grams bromine was added to the mixturedrop-wise through the addition funnel. The temperature was maintained atabout 30° C. or less using an ice bath. Following addition of thebromine, the reaction mixture was stirred for 1 hour at roomtemperature. Reaction completion was determined by gas chromatography,by monitoring the disappearance of the starting material,2-isopropylphenol, and of monobrominated species.

Upon completion of the reaction, 4075 grams of ethyl acetate was added.The mixture was stirred for 15 minutes and then allowed to phase split.The bottom (aqueous) layer was removed and 2765 grams of a 13 wt. %aqueous sodium hydrosulfite solution was added. The mixture was stirredwell and then allowed to phase split. The bottom (aqueous) layer wasremoved and 2842 grams of a 15 wt. % aqueous sodium carbonate solutionwas added. The mixture was stirred well and then allowed to phase split.The bottom (aqueous) layer was removed and solvent was stripped from thetop layer using a rotary evaporator. This procedure providedapproximately 2556 grams of 4,6-dibromo-2-isopropyl phenol (DBiPP).

A 12 liter, four neck, round bottom flask was set up with a mechanicalstirrer, condenser, temperature probe and addition funnel in a coolingbath. 800 grams of 4,6-dibromo-2-isopropyl phenol (DBiPP) was added tothe flask along with 4902 grams of deionized water and 408 grams ofsodium iodide. Using the addition funnel, 435 grams of a 50% sodiumhydroxide solution was added while maintaining the temperature below 25°C. The cooling bath was then removed and the reaction mixture was heatedto reflux (100° C.). Using a clean addition funnel, 744 grams of6-chlorohexanol was added over 1 hour and 30 minutes. The reaction wasmixed 2 more hours at which point gas chromatography (GC) analysisindicated 0.3% of the starting DBiPP remained unreacted. The solutionwas cooled and left at room temperature (22-25° C.) overnight.

4196 grams of ethyl acetate was added to the reaction flask and mixedfor 10 minutes (t-butyl methyl ether or other suitable organic solventmay be used). The mixture was allowed to phase split. The bottom aqueouslayer was removed by vacuum and the pH was recorded at 11. The washingstep was repeated a second time using a solution of 27 grams of 37% HClin 980 grams of deionized water. The aqueous phase that was removed hada pH of 1. The washing step was repeated a third time using 980 grams ofa 3% (w/w) aqueous sodium carbonate solution. Again, the aqueous phasewas removed and the pH was recorded at 11. The final washing was donewith a 4.7% (w/w) aqueous solution of sodium chloride (982 grams). Theaqueous phase was again removed by vacuum. The organic phase filteredand concentrated on a rotary evaporator using a water aspirator.Residual solvent was removed using a vacuum pump while stirring theconcentrate with a magnetic stirrer. 1250 grams of a yellow liquid wasobtained. The yellow liquid was purified by continuous distillationusing a rolled film evaporator. First, 6-chlorohexanol and 6-iodohexanolwere removed at the following conditions: 130° C. oil bath and 5-20microns Hg vacuum. The residue was then continuously distilled on therolled film evaporator using the following conditions: 130° C. oil bathand 1 micron Hg vacuum. 832 grams of the water white alkylated product{6-(4,6-dibromo-2-isopropyl phenoxy)-1-hexanol} was recovered. It can benoted here that optionally, a wiped film evaporator can be used in placeof the rolled film evaporator.

A 5 liter, four neck round bottom flask was equipped with a mechanicalstirrer, Dean Stark trap, condenser, and temperature probe. The flaskwas charged with 600 grams of 6-(4,6-dibromo-2-isopropylphenoxy)-1-hexanol; 2805 grams of toluene; 200 ppm each of methylhydroquinone and hydroquinone; 15.2 grams p-toluene sulfonic acid and131 grams acrylic acid. This mixture was heated to reflux with stirringto azeotrope the water. After 6 hours of refluxing, 30 ml of water hadbeen removed and 99.2% of the 6-(4,6-dibromo-2-iso-propylphenoxy)-1-hexanol had been converted to 6-(4,6-dibromo-2-iso-propylphenoxy)-1-hexyl acrylate based on GC analysis. The solution was thencooled and allowed to mix overnight.

828 grams of a 0.27% HCl solution was added to the reaction flask andmixed for 5 minutes. The mixture was allowed to phase split and theaqueous bottom phase (pH=1) was removed by vacuum. The washing wasrepeated by adding 903 grams of an 8.9% (w/w) aqueous solution of sodiumcarbonate. The aqueous phase was removed after phase separation. A thirdwash was done using 867 grams of a 5.1% (w/w) aqueous sodium chloridesolution. The aqueous phase was again removed by vacuum. The organicphase was filtered and concentrated on a rotary evaporator using a wateraspirator. Residual solvent was removed using a vacuum pump whilestirring the concentrate with a magnetic stirrer. 650 grams of a hazy,light yellow liquid was obtained. The yellow liquid was then purified bycontinuous distillation in a rolled film evaporator using the followingconditions: 175° C. oil bath and 1 micron Hg vacuum to give the waterwhite product. NMR analysis indicated a 98.8% purity prior todistillation and a purity of >99% in the distilled product,6-(4,6-dibromo-2-iso-propyl phenoxy)-1-hexyl acrylate (DBiPPHA).

2. Synthesis of 6-(4,6-dibromo-2-sec-butylphenoxy)-1-hexyl acrylate(DBsBPHA)

The analogous monomer 6-(4,6-dibromo-2-sec-butyl phenoxy)-1-hexylacrylate (DBsBPHA) was prepared in the same manner starting with astoichiometric equivalent amount of 2-sec-butyl phenol rather than the2-isopropylphenol.

3. Synthesis of 2,6-dibromo-4-nonylphenyl acrylate (DBpNPA)

44 grams (0.2 mole) 4-nonylphenol was mixed in a three neck round bottomflask with 180 grams deionized water. The mixture was stirred with amechanical stirrer. The reaction solution was purged well with nitrogen.To the flask, 66 grams (0.41 mole) bromine was added dropwise, keepingthe reaction temperature about 30° C. After completing the addition, thereaction was stirred for ½ hour at room temperature. The reactionprogress was monitored using GC. Because the phenol was a mixture ofisomers, an additional 11 grams of bromine was added to react all thestarting material.

160 grams ethyl acetate was added with stirring and the mixture wasallowed to phase split. The bottom (aqueous) layer was removed. Theorganic layer was washed sequentially with a pre-mix of 3.5 grams sodiumhydrosulfite in 23 grams water and a pre-mix of 3.9 grams sodiumchloride in 26 grams water. For each washing, the aqueous premix wasstirred well with the organic layer, allowed to phase split and thenremoved. After the final washing, the solvent was stripped on a rotaryevaporator to give a yellow oil.

The yellow oil was distilled using a distillation head and shortvigeraux column. The product was distilled at 1.0 mm Hg and a headtemperature of 165-170° C. The yield is 66 grams (87%) of light yellowliquid. Analysis by GC and NMR verified the material to be2,6-dibromo-4-nonylphenol.

30.5 grams (0.08 mole) 2,6-dibromo-4-nonylphenol, 64 grams t-butylmethyl ether, 9.8 grams (0.096 mole) triethyl amine, and 0.005 gramsphenothiazine were mixed in a three neck round bottom flask equippedwith a mechanical stirrer, temperature probe, and addition funnel. 8.4grams (0.092 mole) acryloyl chloride was added dropwise. An ice waterbath was used to keep the reaction temperature below 20° C. GC showscomplete reaction conversion.

45.6 grams deionized water was added, the mixture stirred and allowed tophase split. The lower aqueous phase was removed. The organic layer waswashed sequentially with a pre-mix of 0.2 grams concentrated HCl in 8.7grams deionized water; a pre-mix of 1.7 grams sodium carbonate in 9grams deionized water; and a pre-mix of 0.8 gram NaCl in 9 gramsdeionized water. The aqueous pre-mixes were mixed with the organicphase, allowed to phase split, and then discarded. The organic solutionwas then dried with magnesium sulfate, filtered, and the solvent removedusing a rotary evaporator. This method produced 32 grams (92%) of alight yellow oil which was characterized by NMR and GC analysis.

4. Synthesis of 2,6-dibromo-4-dodecylphenyl acrylate (DBpDDPA)

The reactions were run as outlined above, except a stoichiometricequivalent of 4-dodecylphenol was used instead of 4-nonylphenol.

5. Synthesis of 2-(1-naphthyloxy)-1-ethyl acrylate (1-NOEA)

A 5 liter, three neck round bottom flask was equipped with a temperatureprobe, mechanical stirrer, and condenser. 400 grams 1-naphthol, 269grams ethylene carbonate and 281 grams triethylamine were added to theflask. Using medium agitation, the batch was heated to 95° C. and beganto give off CO₂. The batch was held at this temperature for 12 hours, asample was taken and residual 1-naphthol was determined by GC. Heatingof the batch continued at 95° C. until there was less than 3% residual1-naphthol.

The reaction was then cooled to room temperature and 1470 gramstert-butyl methyl ether and 56 grams triethylamine were added. 0.15 gramhydroquinone and 0.15 gram hydroquinone monomethyl ether were added asinhibitors. To the well-stirred reaction, 289 grams acryloyl chloridewas added over a 2-4 hour period, keeping the batch temperature between25-30° C. The batch was stirred with medium agitation at roomtemperature for 1 hour after completing the addition. A sample was takenand GC run to determine reaction completion (<1% residual2-(1-naphthyloxy)-1-ethanol).

The batch was then cooled to room temperature and then washed, firstwith 400 grams deionized water and 11 grams HCl, then with 250 grams of15% sodium carbonate in water solution, and then with 250 grams of 20%sodium chloride solution. Residual solvent was removed using a rotaryevaporator. The product was a dark colored, low viscosity (<80 cps)liquid (570 grams).

The crude monomer was purified using a continuous a high vacuum rolledfilm evaporator (available from UIC Inc. of Joliet, Ill.) with thefollowing conditions: 110° C. jacket temperature, 30° C. condensertemperature, 40° C. feed temperature, 300 rpm rotor speed, and 1 micronvacuum. The distillation gave an 80-85% product split. The product,1-NOEA (475 grams), was a light yellow to orange liquid and wascharacterized by ¹³C NMR and confirmed to be 95% pure.

6. Synthesis of 6-(1-naphthyloxy)-1-hexyl acrylate (1-NOHA)

A 1 liter, three neck flask was equipped with a mechanical stirrer,temperature probe, and a condenser. The following reagents were added:50 grams 1-naphthol, 312 grams deionized water, 5.2 grams sodium iodide,and 55.4 grams sodium hydroxide (50% solution in water). The mixture washeated to reflux. To the refluxing reaction, 94.7 grams6-chloro-1-hexanol was added dropwise through an addition funnel over a2-hour period. Heating at reflux was continued for an additional hourafter completing the addition. GC analysis showed <1% residual startingmaterial.

The reaction was cooled to room temperature. 366 grams t-butyl methylether was added. The reaction mixture was stirred, then poured into aseparatory funnel, and allowed to phase split. The aqueous phase wasremoved and the organic phase washed with 6.9 grams concentrated HCl in125 grams deionized water, then with 6.1 grams NaCl in 125 gramsdeionized water. The remaining solvent was stripped from the productusing a rotary evaporator.

The product was distilled at a pot temperature of 220-260° C., headtemperature of 200-230° C., at 0.1-0.2 mm Hg. This procedure yielded63.5 grams of a light brown, somewhat viscous liquid. GC showed itwas >98% pure 6-(1-naphthyloxy)-1-hexanol. This material was used in thenext step of the synthesis.

A 1 liter, three neck flask, equipped with a mechanical stirrer,temperature probe, and Dean-Stark trap with condenser was charged withthe following reagents: 60 grams 6-(1-naphthyloxy)-1-hexanol, 226 gramstoluene, 2.5 grams para-toluene sulfonic acid, 21.2 grams acrylic acid,0.027 gram hydroquinone, and 0.03 gram 4-methoxyphenol. The mixture washeated to reflux, collecting the water which evolved in the Dean-Starktrap. After 3 hours, thin layer chromatography showed the reaction iscomplete (i.e., no starting material remained).

The reaction was cooled to room temperature and 132 grams of deionizedwater were added. The mixture was put into a separatory funnel, shakenand allowed to phase split. The aqueous layer was removed and theorganic phase was washed with 0.3 gram concentrated HCl in 44 gramsdeionized water, then with 1.3 grams sodium carbonate in 44 gramsdeionized water, then with 1.4 grams sodium chloride in 44 gramsdeionized water. The remaining solvent was stripped using a rotaryevaporator. The crude product residue was passed through a flash silicagel column eluting with 5% ethyl acetate/95% heptanes. The productfractions were collected and the solvent stripped using a rotaryevaporator. The light greenish oil product crystallized on standing togive 45 grams of off-white crystals with a melting point of 37-39° C. GCand ¹³C NMR analysis confirmed the product to be 99% pure6-(1-naphthyloxy)-1-hexyl acrylate (1-NOHA).

7. Synthesis of 2-phenylthio ethyl acrylate (PTEA)

A 500 ml three neck round bottom flask equipped with a stirrer, vigerauxcolumn and distillation head/receiver was charged with 50 grams (0.32mole) of 2-(phenylthio) ethanol, 139.5 grams (1.62 mole) methylacrylate,0.22 gram dibutyltin diacetate, 0.015 gram NPAL and 0.015 gram4-methoxyphenol. The reaction flask was heated to 100° C. to distill offan azeotrope of methanol and methylacrylate. As the distillationsubsided, 150 grams of methylacrylate was added to the flask. Thisaddition procedure was repeated two more times.

Gas chromatographic analysis of the reaction mixture showed <1%unreacted 2-(phenylthio)ethanol. The reaction mixture was then cooled to50° C. and the residual methylacrylate was removed by vacuumdistillation. The product, 2-phenylthio ethyl acrylate (50 grams), was ayellow liquid and was characterized by ¹³C NMR to be 97% pure.

Preparation of PSAs

The PSAs of the present invention can be made by solution, emulsion orbulk polymerization methods. The procedures for these polymerizationmethods are described below as Method A, Method B, and Method C,respectively.

Method A—Solution Polymerization

Comparative Example C-1 and Examples 1-14 were prepared using a solutionpolymerization method. All components were weighed into a glass bottlehaving a 120 gram capacity. The contents of the bottles weredeoxygenated by purging with nitrogen at a flow rate of 1 liter perminute for 35 seconds. The bottles were sealed and placed in a rotatingwater bath at 57° C. for 24 hours to effect essentially completepolymerization. The polymer solutions were coated onto a 37 micrometer(1.5 mil) polyester film to provide a dry coating thickness of 25micrometers (˜1 mil). The coated film was equilibrated and thereaftertested under conditions of about 23° C. and 50% relative humidity asdescribed by the shear and adhesion test methods. Equilibrated filmswere utilized to measure refractive index.

Method B—Emulsion Polymerization

Examples 15 and 16 were prepared using an emulsion polymerization method(Method B). All components were added to a 500 ml beaker and mixed untilthe aqueous and organic phases were homogeneous. The mixture was thenhomogenized in a Waring Blender for 2 minutes to prepare emulsions forpolymerization. The emulsions were placed in glass bottles having a 120gram capacity. The contents of the bottles were deoxygenated by purgingwith nitrogen at a flow rate of 1 liter per minute for about 2 minutes.The bottles were sealed and placed in a rotating water bath at 60° C.for 24 hours to effect essentially complete polymerization. Afterpolymerization, the latexes were filtered through cheesecloth to removecoagulum before coating and evaluation. The polymer latexes were coatedonto a 37 micrometer (1.5 mil) polyester film to provide a dry coatingthickness of about 25 micrometers (˜1 mil). The coated films wereequilibrated and thereafter tested under conditions of about 23° C. and50% relative humidity as described by the shear and adhesion testmethods. Equilibrated films were utilized to measure refractive index.

Method C—Bulk Polymerization

Examples 17-29 and Comparative Example C-2 were prepared using a bulkpolymerization method (Method C). The monomer components were mixed in250 ml glass bottles to which was added CBr₄ (0.2% of total monomerweight) and IRGACURE™ 651 (0.1% of total monomer weight). The contentsof the bottles were thoroughly mixed and deoxygenated by purging withnitrogen at a flow rate of 1 liter per minute for 2 minutes. Using aknife coater, the mixtures were coated to a thickness of about 50-80micrometers (˜2-3 mils) between a primed 38 micrometer (1.5 mil)polyester film and a release liner. The resulting coatings werepolymerized using ultraviolet radiation under a fluorescent black light(about 680 millijoules/cm²) for about 10 minutes. The coated film wasequilibrated and thereafter tested under conditions of about 23° C. and50% relative humidity as described by the shear and adhesion testmethods. Equilibrated films were utilized to measure refractive index asnoted above.

Comparative Example C-1 (BA/AA 92.5/7.5)

16.65 grams butyl acrylate, 1.35 grams acrylic acid, 42 grams acetone,and 0.036 grams VAZO™ 67 free radical initiator were charged into aglass bottle and polymerized as described in Method A. Measured % solidswas 28.0%. Refractive index, shear, and adhesion results are given inTable II.

Example 1 (BA/AA/1-NOHA 72.5/7.5/20)

13.05 grams butyl acrylate, 3.6 grams 1-NOHA, 1.35 grams acrylic acid,42 grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described in Method A.Measured % solids were 26.9%. Refractive index, shear, and adhesionresults are given in Table II.

Example 2 (BA/AA/1-NOHA 52.5/7.5/40)

9.45 grams butyl acrylate, 7.2 grams 1-NOHA, 1.35 grams acrylic acid, 42grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described according toMethod A. Measured % solids was 26.4%. Refractive index, shear, andadhesion results are given in Table II.

Example 3 (BA/AA/1-NOEA 72.5/7.5/20)

13.05 grams butyl acrylate, 3.6 grams 1-NOEA, 1.35 grams acrylic acid,42 grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into glass bottle and polymerized as described in Method A.Measured % solids were 28.29%. Refractive index, shear, and adhesionresults are given in Table II.

Example 4 (BA/AA/1-NOEA 52.5/7.5/40)

9.45 grams butyl acrylate, 7.2 grams 1-NOEA, 1.35 grams acrylic acid, 42grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described in Method A.Measured % solids was 29.8%. Refractive index, shear, and adhesionresults are given in Table II.

Example 5 (BA/AA/1-NOEA 85.5/7.5/7)

15.39 grams butyl acrylate, 1.26 grams 1-NOEA, 1.35 grams acrylic acid,42 grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described in Method A.Measured % solids were 27.5%. Refractive index, shear, and adhesionresults are given in Table II.

Example 6 (BA/AA/1-NOEA 82.5/7.5/10)

14.85 grams butyl acrylate, 1.8 grams 1-NOEA, 1.35 grams acrylic acid,42 grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described in Method A.Measured % solids was 27.5%. Refractive index, shear, and adhesionresults are given in Table II.

Example 7 (BA/AA/1-NOEA 79.5/7.5/13)

14.31 grams butyl acrylate, 2.34 grams 1-NOEA, 1.35 grams acrylic acid,42 grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described in Method A.Measured % solids were 27.6%. Refractive index, shear, and adhesionresults are given in Table II.

Example 8 (BA/AA/DBpNPA 72.5/7.5/20)

13.05 grams butyl acrylate, 3.6 grams DBpNPA, 1.35 grams acrylic acid,42 grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described in Method A.Measured % solids was 29.0%. Refractive index, shear, and adhesionresults are given in Table II.

Example 9 (BA/AA/DBpNPA 52.5/7.5/40)

9.45 grams butyl acrylate, 7.2 grams DBpNPA, 1.35 grams acrylic acid, 42grams acetone, and 0.036 grams VAZO™ 67 free radical initiator werecharged into a glass bottle and polymerized as described in Method A.Measured % solids was 28.0%. Refractive index, shear, and adhesionresults are given in Table II.

Example 10 (BA/AA/DBiPPHA 68/2/30)

11.42 grams butyl acrylate, 5.04 grams DBiPPHA, 0.34 grams acrylic acid,42.7 grams ethyl acetate, 0.432 grams isopropyl alcohol, and 0.025 gramsVAZO™ 67 free radical initiator were charged into a glass bottle andpolymerized as described according to Method A. 0.1% by weightN,N′-bis-1,2-propyleneisophthalamide crosslinker was added to just priorto coating. Refractive index, shear, and adhesion results are given inTable II.

Example 11 (BA/AA/DBiPPHA 38/2/60)

6.38 grams butyl acrylate, 10.08 grams DBiPPHA, 0.34 grams acrylic acid,42.3 grams ethyl acetate, 0.864 grams isopropyl alcohol, and 0.025 gramsVAZO™ 67 free radical initiator were charged into a glass bottle andpolymerized as described according to Method A. 0.1% by weightN,N′-bis-1,2-propyleneisophthalamide crosslinker was added to just priorto coating. Refractive index, shear, and adhesion results are given inTable II.

Example 12 (TOA/AA/PTEA 68/2/30)

16.32 grams iso-octyl acrylate, 7.2 grams PTEA, 0.48 grams acrylic acid,36 grams ethyl acetate, and 0.048 grams VAZO™ 67 free radical initiatorwere charged into a glass bottle and polymerized as described accordingto Method A. Refractive index, shear, and adhesion results are given inTable II.

Example 13 (IOA/AA/PTEA 58/2/40)

13.92 grams iso-octyl acrylate, 9.6 grams PTEA, 0.48 grams acrylic acid,36 grams ethyl acetate, and 0.048 grams VAZO™ 67 free radical initiatorwere charged into a glass bottle and polymerized as described accordingto Method A. Refractive index, shear, and adhesion results are given inTable II.

Example 14 (IOA/AA/PTEA 48/2/50)

11.52 grams iso-octyl acrylate, 12 grams PTEA, 0.48 grams acrylic acid,36 grams ethyl acetate, and 0.048 grams VAZO™ 67 free radical initiatorwere charged into a glass bottle and polymerized as described accordingto Method A. Refractive index, shear, and adhesion results are given inTable II.

Example 15 (BA/AA/1-NOEA 75/5/20)

37.4 grams deionized water, 0.40 gram RHODOCAL DS-10™, 18.75 grams butylacrylate, 5.0 grams 1-NOEA, 1.25 grams acrylic acid, and 0.05 gramK₂S₂O₈ were mixed, emulsified and polymerized as described in Method B.Refractive index, shear, and adhesion results are given in Table II.

Example 16 (BA/AA/1-NOEA 61/6/33)

37.4 grams deionized water, 0.40 gram RHODOCAL DS-10™, 13.75 grams butylacrylate, 7.5 grams 1-NOEA, 1.25 grams acrylic acid, and 0.05 gramK₂S₂O₈ were mixed, emulsified and polymerized as described in Method B.Refractive index, shear, and adhesion results are given in Table II.

Examples 17-29 and Comparative Example C-2

Comparative Example C-2 and Examples 17-29 were prepared according toMethod C using the monomer components noted in Table I below. A premixsyrup of 90 parts IOA and 10 parts AA was prepared for these examples.All values in Table I are parts by weight based on a total of 100 partsmonomer. Refractive index, shear, and adhesion results are given inTable II. TABLE I IOA/AA Syrup Example (90/10) DBiPPHA DBsBPHA PEA C-2100 17 80 20 18 60 40 19 40 60 20 20 80 21 100 22 80 20 23 60 40 24 4060 25 20 80 26 100 27 80 20 28 60 40 29 40 60

Example 30 (DBsBPHA/EB-9220 99/1)

A PSA adhesive composition was prepared by mixing 99 parts DBsBPHA, 1part EB-9220, a hexa-functional aromatic urethane acrylate, and 1.5parts of TPO photoinitiator (1.5% of total monomer weight) in anappropriately sized container. The mixture was warmed to 65° C. for 15minutes and then mixed again. The mixture was coated on a polyester filmusing a knife coater to a thickness of approximately 25 microns. Thecoated film construction was passed under a 300 watt/cm UV lamp at aspeed of 20 ft/min (6.1 m/min) and then heated in a 100° C. oven for 1minute. Refractive index, shear, and adhesion results are given in TableII.

Example 31 (DBiPPHA/EB-9220 99/I)

A PSA adhesive composition was prepared as described in Example 30 withthe exception that DBiPPHA was used instead of DBsBPHA. Refractiveindex, shear, and adhesion results are given in Table II. TABLE IIExample Adhesion Formula PSA Type Refractive Index Shear (min) N/100 mmComparative Example C-1 Solution 1.4684    4.75 71 BA/AA (92.5/7.5)Example 1 Solution 1.4913    10.80 59 BA/AA/1-NOHA(72.5/7.5/20) Example2 Solution 1.5141    32.80 69 BA/AA/1-NOHA(52.5/7.5/40) Example 3Solution 1.4978    57.80 74 BA/AA/1-NOEA (72.5/7.5/20) Example 4Solution 1.5236   749 15 BA/AA/1-NOEA(52.5/7.5/40) Example 5 Solution1.4795    38 67 BA/AA/1-NOEA (85.5/7.5/7) Example 6 Solution 1.4848   39 70 BA/AA/1-NOEA (82.5/7.5/10) Example 7 Solution 1.4902    36 77BA/AA/1-NOEA (79.5/7.5/13) Example 8 Solution 1.4900   125 17BA/AA/DBpNPA (72.5/7.5/20) Example 9 Solution 1.5137   3842 2BA/AA/DBpNPA (52.5/7.5/40) Example 10 Solution 1.4886    9.0 55BA/AA/DBiPPHA (68/2/30) Example 11 Solution 1.5148    5 81 BA/AA/DBiPPHA(38/2/60) Example 12 Solution 1.5007    5.35 67 IOA/AA/PTEA (68/2/30)Example 13 Solution 1.5112    6.90 68 IOA/AA/PTEA (58/2/40) Example 14Solution 1.5256    6.80 64 IOA/AA/PTEA (48/2/50) Example 15 Emulsion1.4963    70 52 BA/AA/1-NOEA (75/5/20) Example 16 Emulsion 1.5176   23047 BA/AA/1-NOEA (61/6/33) Comparative Example C-2 Bulk 1.4704   105 69IOA/AA (90/10) Example 17 Bulk 1.4841    40 75 IOA/AA/DBiPPHA (72/8/20)Example 18 Bulk 1.4965  4,000 82 IOA/AA/DBiPPHA (54/6/40) Example 19Bulk 1.5134  7,600 90 IOA/AA/DBiPPHA (36/4/60) Example 20 Bulk 1.5309 2,500 91 IOA/AA/DBiPPHA (18/2/80) Example 21 Bulk 1.5568  3,200 63DBiPPHA (100) Example 22 Bulk 1.4834 10,000+ 62 IOA/AA/DBsBPHA (72/8/20)Example 23 Bulk 1.4976 10,000+ 57 IOA/AA/DBsBPHA (54/6/40) Example 24Bulk 1.5132 10,000+ 60 IOA/AA/DBsBPHA (36/4/60) Example 25 Bulk 1.5283 7,600 48 IOA/AA/DBsBPHA (18/2/80) Example 26 Bulk 1.5532 10,000+ 40DBsBPHA (100) Example 27 Bulk 1.4856 10,000+ 46 IOA/AA/PEA (72/8/20)Example 28 Bulk 1.4976 10,000+ 48 IOA/AA/PEA (54/6/40) Example 29 Bulk1.5154 10,000+ 51 IOA/AA/PEA (36/4/60) Example 30 Bulk 1.5544   914 37DBsBPHA/EB-9220 (99/1) Example 31 Bulk 1.5580   1079 30 DBiPPHA/EB-9220(99/1)

Various modifications and alterations to this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention. It should be understood that thisinvention is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of theinvention intended to be limited only by the claims as set forth hereinas follows.

1. A pressure-sensitive adhesive comprising an aromatic monomer in anamount of at least 20 parts per 100 parts of total monomer, the aromaticmonomer having the following formula:

wherein: Ar is an aromatic group which is substituted with a substituentselected from the group consisting of Br_(y) and (R³)_(z) wherein yrepresents the number of bromine substituents attached to the aromaticgroup and is an integer from 0 to 3; R³ is a straight or branched alkylof 2 to 12 carbons; and z represents the number of R³ substituentsattached to the aromatic ring and is an integer from 0 to 1, providedthat both y and z are not zero when Ar is substituted; X is oxygen orsulfur; n is 1 to 3; R¹ is an unsubstituted straight or branched alkyllinking group of 6 to 12 carbons; and R² is either H or CH₃.
 2. Thepressure-sensitive adhesive according to claim 1, wherein z is 1 and R³is a straight or branched alkyl of 2 to 8 carbons.
 3. Thepressure-sensitive adhesive according to claim 1, wherein Ar is anaphthyl group.
 4. The pressure-sensitive adhesive according to claim 1,wherein n is
 1. 5. The pressure-sensitive adhesive according to claim 1,wherein X is oxygen.
 6. The pressure-sensitive adhesive according toclaim 1, wherein the refractive index is at least 1.48.
 7. Thepressure-sensitive adhesive according to claim 1, wherein the refractiveindex is at least 1.50.
 8. The pressure-sensitive adhesive according toclaim 1, further comprising: at least one acrylic monomer selected fromthe group consisting of monomeric acrylic or methacrylic acid ester of anon-tertiary alkyl alcohol of about 1 to about 12 carbons.
 9. Thepressure-sensitive adhesive according to claim 8, wherein the acrylicmonomer is selected from the group consisting of 1-butanol, 1-pentanol,2-pentanol, 3-pentanol, 2-methyl-1-butanol, 1-methyl-1-butanol,1-methyl-1-pentanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol,2-ethyl-1-butanol, 2-ethyl-1-hexanol, 3,5,5-trimethyl-1-hexanol,3-heptanol, 2-octanol, 1-decanol, 1-dodecanol, and mixtures thereof. 10.The pressure-sensitive adhesive according to claim 1, further comprisingat least one polar monomer copolymerizable with the aromatic monomer(s).12. The pressure-sensitive adhesive according to claim 10, wherein thepolar monomer(s) are selected from the group consisting of ethylenicallyunsaturated carboxylic acids, ethylenically unsaturated sulfonic acids,ethylenically unsaturated phosphoric acids, acrylamides, N,N-dialkylsubstituted acrylamides, N-vinyl lactams, and N,N-dialkylaminoalkylacrylates, ethylenically unsaturated nitriles, and mixtures thereof. 13.The pressure-sensitive adhesive according to claim 10, wherein the polarmonomer(s) are selected from the group consisting of acrylic acid,methacrylic acid, itaconic acid, acrylamide, methacrylamide,acrylonitrile, methacrylonitrile, and mixtures thereof.
 14. Thepressure-sensitive adhesive according to claim 1, further comprising: atleast one acrylic monomer selected from the group consisting ofmonomeric acrylic or methacrylic acid ester of a non-tertiary alkylalcohol of about 1 to about 12 carbons, and at least one polar monomercopolymerizable with the aromatic monomer(s) and acrylic monomer(s). 15.The pressure-sensitive adhesive according to claim 1, wherein thearomatic monomer is selected from the group consisting of6-(4,6-dibromo-2-isopropyl phenoxy)-1-hexyl acrylate and6-(4,6-dibromo-2-sec-butyl phenoxy)-1-hexyl acrylate.
 16. Thepressure-sensitive adhesive according to claim 1, further comprising acrosslinker.
 17. The pressure-sensitive adhesive according to claim 1,further comprising one or more monomers selected from the groupconsisting of vinyl esters, vinyl acetate, 2-hydroxyethyl acrylate,styrene, and mixtures thereof.
 18. The pressure-sensitive adhesiveaccording to claim 1, further comprising a tackifier.
 19. Thepressure-sensitive adhesive according to claim 1, further comprising aplasticizer.
 20. A pressure-sensitive adhesive having an index ofrefraction of at least 1.50 and comprising an aromatic monomer havingthe following formula:

wherein: Ar is napthyl which is unsubstituted or substituted with asubstituent selected from the group consisting of Br_(y) and (R³)_(z)wherein y represents the number of bromine substituents attached to thearomatic group and is an integer from 0 to 3; R³ is a straight orbranched alkyl of 2 to 12 carbons; and z represents the number of R³substituents attached to the aromatic ring and is an integer from 0 to1, provided that both y and z are not zero when Ar is substituted; X isoxygen or sulfur; n is 1 to 3; R¹ is an unsubstituted straight orbranched alkyl linking group of 2 to 12 carbons; and R² is either H orCH₃; copolymerized with at least one acrylic monomer selected from thegroup consisting of monomeric acrylic or methacrylic acid ester of anon-tertiary alkyl alcohol of about 4 to about 12 carbons and at leastone polar monomer copolymerizable with the aromatic monomer(s) andacrylic monomer(s).